Sleeping cells are a special case of cell outage which makes mobile services unavailable for subscribers, while from the network point of view the network still appears to be operable. In this case, no service is provided to the end user, but no alarm is sent to the Operation and Maintenance Center (OMC) to indicate the problem.
Having sleeping cells in the network is a large problem for the network operator, since it can take a long time before the fault is detected. A thorough analysis of changes in traffic patterns over time may be needed in order to detect the malfunction. Such an analysis requires skilled personnel and takes time. Sleeping cells are thus costly for operators both because of the loss of revenue and because of the difficulty of detection. Furthermore the operator's reputation may be damaged if end users perceive the network as unreliable.
A common cause of sleeping cells is that the downlink (DL) transmissions fail, and in this area there are a number of existing strategies for detecting sleeping cells, such as using User Equipment (UE) measurements to detect sleeping cells e.g. Reference Signal Received Power (RSRP) and Reference Signal Received Quality (RSRQ) measurements that are collected from the UE and are fed to a centralized node to detect an outage of a cell.
In a more uncommon case, DL transmissions in the cell are still functional, but uplink (UL) reception fails. Normally, UL only failures are detected using statistical methods such as low wideband Received Signal Strength (RSS) measured by baseband.
Most of the existing solutions for detecting sleeping cells target the case when the DL transmission fails. They fail to address the case when DL transmission is unaffected, and the problem is in UL reception. Methods today for uplink failure are mostly statistical methods based on measured RSS. A drawback of these methods is that they are unreliable and time consuming.